A method and system of time-to-intercept determination for a radiation source using passively-sensed irradiance data. The invention provides a plurality of noise reduction features to reduce the noise present in the data and improve the accuracy of the time-to-intercept computation. The method includes reducing data noise by defining an acceptable noise level and eliminating any excessively noisy data from the time-to-intercept computation. The method further includes constantly updating the time-to-intercept computation by using irradiance values that are advanced in time. Other features of the present invention includes averaging of irradiance values over a time interval, filtering of the irradiance data received by the method, and triggering at a predetermined time-to-intercept. The invention also includes a time-to-intercept system and processor implementing the above method.
Legal claims defining the scope of protection, as filed with the USPTO.
1. A method of determining a time-to-intercept for a radiation source using irradiance values of the radiation source, the method comprising: computing the time-to-intercept using at least three irradiance values; and reducing noise in the time-to-intercept computation by using a continuously-updated calculation, based upon recent values, and upon initial values; where, performing the calculation comprises determining a signal-to-noise ratio (SNR) value of each irradiance value and rejecting from the calculation an irradiance value having a SNR value that is less than a threshold SNR value.
2. The invention as set forth in claim 1 , wherein each irradiance value is a respective detected irradiance value of the radiation source.
3. The invention as set forth in claim 1 , wherein the threshold signal-to-noise ratio value can be 27 decibels.
4. The invention as set forth in claim 1 , further comprising: filtering of each irradiance value to reduce noise in the irradiance values.
5. The invention as set forth in claim 4 , wherein: filtering of the irradiance values is continuous; and each irradiance value is a respective detected irradiance value of the radiation source.
6. The invention as set forth in claim 1 , further comprising: determining whether a time interval between irradiance values is greater than a minimum time interval; computing an average irradiance value over the time interval if the time interval is greater than the minimum time interval.
7. The invention as set forth in claim 1 , wherein calculating the time-to-intercept further comprises: using an equation relating the irradiance values to the time-to-intercept.
8. The invention as set forth in claim 7 , wherein the equation uses signal strength normalization.
9. The invention as set forth in claim 8 , wherein: signal strength normalization includes having a ratio of the irradiance values; each irradiance value is a respective radiation intensity value of the radiation source.
10. The invention as set forth in claim 7 , wherein the equation is derived using a constant acceleration assumption.
11. The invention as set forth in claim 7 , wherein the equation is derived using a constant velocity assumption.
12. The invention as set forth in claim 1 , wherein computing the time-to-intercept further comprises: computing a first time-to-intercept value using first and second irradiance values; and updating the time-to-intercept by computing a second time-to-intercept value using a third irradiance value taken later in time than the first and the second irradiance values.
13. The invention as set forth in claim 12 , further comprising: repeating the time-to-intercept updating with subsequent irradiance values that are later in time until a predetermined time-to-intercept value is reached.
14. A method for determining a time-to-intercept for a radiation source, comprising: providing irradiance data relating to the radiating source; minimizing noise associated with the irradiance data so as to provide usable irradiance data; computing the time-to-intercept using the usable irradiance data; and updating the time-to-intercept computation using updated usable irradiance data derived from the updated irradiance data; where, minimizing noise comprises determining a signal-to-noise ratio (SNR) value of each irradiance value and declaring an irradiance value to be a usable irradiance value if the SNR value is greater than a threshold SNR value.
15. The invention as set forth in claim 14 , wherein irradiance data includes a detected irradiance of the radiation source.
16. The invention as set forth in claim 14 , wherein irradiance data is provided as one of: (a) a continuous data stream; or (b) a periodically sampled data set; or (c) an aperiodically sampled data set.
17. The invention as set forth in claim 14 , wherein computing the time-to-intercept further comprises using an equation having signal strength normalization.
18. The invention as set forth in claim 17 , wherein the equation assumes a constant acceleration.
19. The invention as set forth in claim 17 , wherein the equation assumes a constant velocity.
20. The invention as set forth in claim 17 , further comprising: computing a time interval between successive usable irradiance data; comparing the time interval to a minimum time interval; and averaging the irradiance data over the time interval if the time interval is approximately less than the minimum time interval.
21. A system for determining a time-to-intercept of a radiation source, comprising: a detection system detecting successive irradiance values of the radiation source; a calculation module that calculates the time-to-intercept using the irradiance values output from said detection system; and an update module that updates the time-to-intercept calculation using irradiance values that are advanced in time; said detection system comprising a noise module for determining a signal-to-noise ratio (SNR) value of each detected successive irradiance value and for outputting to said calculation module only those irradiance values having a SNR value that is greater than a threshold SNR value.
22. The invention as set forth in claim 21 , further comprising: an averaging module that averages irradiance values over a time interval.
23. The invention as set forth in claim 22 , wherein the irradiance value is a detected irradiance of the radiation source.
24. The invention as set forth in claim 22 , wherein the calculation module uses an equation that assumes constant acceleration.
25. The invention as set forth in claim 22 , wherein the calculation module uses an equation that assumes constant velocity.
26. A time-to-intercept processor for determining a time-to-intercept of a radiation source, comprising: means for providing irradiance values of the radiance source successively in time; means for reducing noise present in the irradiance values to produce usable irradiance values, said noise reducing means comprising means for determining a signal-to-noise ratio (SNR) value of each irradiance value and declaring an irradiance value to be a usable irradiance value if the SNR value is greater than a threshold SNR value; and means for calculating the time-to-intercept using the usable irradiance values.
27. The invention as set forth in claim 26 , further comprising: means for averaging the us able irradiance values over a time interval if the time interval is less than a minimum time interval.
28. The invention as set forth in claim 26 , further comprising: an update module for updating the time-to-intercept calculation using irradiance values that are advanced in time.
29. The invention as set forth in claim 28 , wherein the means for providing irradiance values is an input module that inputs irradiance values into the time-to-intercept processor.
30. The invention as set forth in claim 29 , wherein the input module inputs irradiance values as at least one of: (a) a continuous data stream; (b) a periodically sampled data set; (c) an aperiodically sampled data set.
31. The invention as set forth in claim 26 , wherein the means for calculating comprises a calculation module that uses an equation relating the irradiance values to the time-to-intercept.
32. The invention as set forth in claim 31 , wherein a constant acceleration is assumed.
33. The invention as set forth in claim 31 , wherein a constant velocity is assumed.
34. The invention as set forth in claim 31 , wherein the irradiance value is a radiation intensity of the radiation source.
35. A method for determining a time-to-intercept during a time-of-flight of a radiating source, comprising: computing a plurality of irradiance values from measurements made from the radiating source, each computation of the irradiance value using a substantially constant value of acceleration a of the radiating source; reducing noise in the irradiance values to provide usable irradiance values; and computing the time-to-intercept based on usable irradiance values.
36. A method as in claim 35 , where reducing noise comprises determining a signal-to-noise ratio (SNR) value of each irradiance value and declaring an irradiance value to be a usable irradiance value if the SNR value is greater than a threshold SNR value.
37. A method for determining a time-to-intercept during a time-of-flight of a radiating source, comprising: computing, using a substantially constant value of acceleration a of the radiating source, a measured amplitude Z(t) of an irradiance value H(t) from a measurement made from the radiating source; determining a ratio of the measured amplitude to a change in amplitude dZ(t)/dt; and relating the determined ratio dZ(t)/dt to the time-to-intercept of the radiating source.
38. A method as in claim 37 , where the step of computing includes determining a signal-to-noise ratio (SNR) value of each irradiance value and declaring an irradiance value to be a usable irradiance value if the SNR value is greater than a threshold SNR value.
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January 19, 2000
November 26, 2002
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